You're right to think about the freezing point depression! Here's why a 1.5 m CaCl₂ solution would likely have a lower freezing point than a 1.5 m NaCl solution:

Freezing Point Depression and Colligative Properties

* Colligative Properties: These are properties of solutions that depend only on the *concentration* of solute particles, not their identity. Freezing point depression is one such property.

* Freezing Point Depression: The freezing point of a solvent is lowered when a solute is dissolved in it. The greater the concentration of solute particles, the greater the depression.

The Role of Dissociation

* NaCl: Sodium chloride (NaCl) dissociates into two ions in solution: Na⁺ and Cl⁻. So a 1.5 m NaCl solution will have 3.0 m of total ions (1.5 m Na⁺ + 1.5 m Cl⁻).

* CaCl₂: Calcium chloride (CaCl₂) dissociates into three ions in solution: Ca²⁺ and 2Cl⁻. Therefore, a 1.5 m CaCl₂ solution will have 4.5 m of total ions (1.5 m Ca²⁺ + 3.0 m Cl⁻).

The Key Difference

Because CaCl₂ produces more ions in solution than NaCl at the same molality, it will have a greater effect on lowering the freezing point.

In Summary

The 1.5 m CaCl₂ solution will have a lower freezing point than the 1.5 m NaCl solution because it produces a higher concentration of solute particles, leading to a greater depression of the freezing point.